Field of the Invention
This invention relates to a constant current circuit and an integrated circuit having said circuit, particularly to a constant current circuit and an integrated circuit having said circuit which can be suitably used in an analog integrated circuit.
Various circuits have been proposed up to date as the constant current circuit to be used in analog integrated circuits.
FIG. 1 shows a circuit showing an example of the constant current circuit of the prior art. In the Figure, T.sub.a, T.sub.b and T.sub.1 -T.sub.3 represent transistors, Z.sub.1 -Z.sub.3 loads and R.sub.a, R.sub.b and R.sub.1 -R.sub.3 resistors. I.sub.1 -I.sub.3 are constant currents obtained in the circuit shown in FIG. 1. Such constant current circuit makes I.sub.1 -I.sub.3 constant currents respectively by setting T.sub.1 and R.sub.1, T.sub.2 and R.sub.2, and T.sub.3 and R.sub.3 based on the bias potential V.sub.b set by the transistor T.sub.a and T.sub.b, and resistors R.sub.a and R.sub.b, not depending on fluctuations of Z.sub.1 -Z.sub.3.
Also, FIG. 2 shows another example of the constant current circuit of the prior art. In the Figure, T.sub.a, T.sub.b, T.sub.1 and T.sub.2 each represent a transistor, Z.sub.1 and Z.sub.2 each a load, I.sub.1 and I.sub.2 each a constant current obtained in the circuit shown in FIG. 2, and R.sub.a and R.sub.b each a resistor. Also in such constant current circuit, constant currents I.sub.1 and I.sub.2 are obtained on the basis of the bias potential V.sub.b generated by setting of I.sub.o with the band gap output voltages V.sub.BG and R.sub.a.
However, the constant current circuits of the prior art as mentioned above had the following tasks.
(1) In the constant current circuit shown in FIG. 1, errors of current values occur due to variance in characteristics of the transistors, whereby desired constant currents cannot be sometimes obtained with good precision. Also, for solving this problem, the choice of transistors is required or a more complicated circuit construction is required.
(2) In the constant current circuit shown in FIG. 2, because a band gap circuit and an amplifier circuit are required, the circuit scale is large and complicated.